If you use button heads as suggested earlier Torx type heads are more positive than hex,not sure if the go small enough for a grub screw at your size
Stuart

On my bell motors the grub screws always fail. I have had motors come out of the mount in flight and make a mess of the cowling. So, I always take the grub (set) screws out of a new motor and replace them with high quality button head or torx head screws. There is no real need for set screws in this application and either 2.5mm or 3mm screws with hex or torx head work fine.

Also, don't use thread locker like the permanent or semi-permanent blue Loctite because it is much harder to break free when you need to fix something. Use what the military uses, a sealant that will hold tight but never fully hardens and can be re-fastened about 7 times without re-application.

Find a fastener supplier that can sell you the best screws and the thread locker. Such as:

Thanks for the link, never scene that stuff sounds like a good idea. I checked out the site for 2.5mm set screws and they start the metric selection at 3mm. I been searching for 2.5mmX.45mmX5mm set screw, but the only site I found sells the screws for 18 cents and $10.00 shipping. OR 100 screws(brass point?) for $180.00,, buck eighty a screw~!! I have also searched for a combo kit, nothing in small sizes.

Thanks for the link, never scene that stuff sounds like a good idea. I checked out the site for 2.5mm set screws and they start the metric selection at 3mm. I been searching for 2.5mmX.45mmX5mm set screw, but the only site I found sells the screws for 18 cents and $10.00 shipping. OR 100 screws(brass point?) for $180.00,, buck eighty a screw~!! I have also searched for a combo kit, nothing in small sizes.

M2.5's can be troublesome. Try a short hex cap screw. The cap screw will have a bigger hex that is not going to strip as easily as a grub screw. Also the stainless ones are generally harder.

Thanks for the link, never scene that stuff sounds like a good idea. I checked out the site for 2.5mm set screws and they start the metric selection at 3mm. I been searching for 2.5mmX.45mmX5mm set screw, but the only site I found sells the screws for 18 cents and $10.00 shipping. OR 100 screws(brass point?) for $180.00,, buck eighty a screw~!! I have also searched for a combo kit, nothing in small sizes.

Most "grub screws" are secured by some brand of thread-locking compound. Sometimes weak, sometimes strong. Grub screws should always be locked with some type of compound.

Given this...the screws should not be easily removable without additional measures. The most common approach is to place the tip of a soldering iron into the screw cavity for 5-10 seconds before an attempt to remove the screw.

Sure the slop and incorrect choice of wrench complicates the issue and leads to frustration but...if you haven't loosened the sealant those issues become secondary.

Thanks for the suggestions. Unfortunately there is not enough material in this bell to oversize the hole to 3mm. I checked my local Ace, which just did a reset of the store and added lots of hrdwr. they start at 2mm and skip to 3mm. But thanks the good idea's for future reference. My LHS has been so useless for so long I forgot about them as a possibility, I know they carry car stuff. I looked Mcmaster, wow great selection I had no idea there were so many choices in tips. I like the mil-spec stuff. The price is right at penny's a screw but still have to buy a hundred. I'm pondering the idea of buying them and reselling for cost + a postage stamp.

Thanks payne9999 for the info on Vibra-tite VC-3. I sent for some. Hadn't heard of it before.

No problem, I like it because it is removable/serviceable and reusable. I have used it in engineering to secure #2-56 screws all the way to 1/2" bolts on trucks and military vehicles. It works in almost any application except where high temps are involved.

It is a little spendy but for model building a bottle will last a lifetime. Follow the application instructions because it doesn't take much to do the job. The most common problem is using too much.

Thanks Dave, I found it in a smaller size (5 ml) for $7.49, free shipping, and figured that would probably do a lot of motor set screws!

Also found 6mm button heads 2.5mm x 6mm, twenty for $6 so that should take care of 20 motors, all told. Shipping adds some, but one less wrecked plane would more than cover it.

Sounds good and you are correct. Almost lost my DC-6B from a motor that left it's mount. Tore up the nacelle and forced an emergency landing. I have grown to hate those kind of motor mounts. However, if one replaces the setscrews with high quality button, pan or cap head screws and good locking compound it should be fine. The other weak link is sometimes those mounts have barely enough wall thickness to get 2-3 threads of engagement so they tend to strip easy. So, when you have a screw that can develop better torque watch out that you don't turn them too hard and strip the threads.

Last time I sharpened the ends of the screws so they would bite in better.

I had never heard of the VC-3 before either. I have been using a number of anerobic locking compounds for many years. Primarily the various flavors of Loctite (blue, green, red for the most part). I understand those and how to use them and what tools and procedures to use to get them loose later.

VC-3 is an acrylic polymer and is a resilient plastic in it's cured form. It has a temp spec of -65˚F to +165˚F (-54˚C to +74˚C) which is a lot less heat than Loctite will handle.

According to the MSDS for VC-3, it can be dissolved with Methyl Ethyl Ketone (MEK) so putting a drop of that on should make removal easier than having to use heat. More details on it here:

Now that I have seen those pics of the product I recognize it. Loctite makes a similar product their version is called it Patch Loc. It comes pre-applied on critical engine fasteners (replacements ), some of the parts are internal to the engine (on the brand of engines I work on ). So I would imagine it has a higher temp range.